An internal combustion engine may be equipped with an air charging system for supplying air into the combustion chambers. The air charging system conventionally includes an intake pipe that provides air from the ambient environment to an intake manifold in fluid communication with each of the combustion chambers through at least one intake port. An intake valve is disposed in the intake pipe with an actuator arranged to move a valve member to regulate the flow of air towards the intake manifold.
The air charging system may also include a turbocharger to force the air into the intake manifold. The turbocharger generally includes a compressor rotationally coupled to a turbine. The compressor is disposed in the intake pipe. The turbine is disposed in an exhaust pipe in fluid communication with an exhaust manifold. In this way, the turbine rotates by receiving exhaust gasses from the exhaust manifold and drives the compressor to increase rotation and the pressure and temperature of the air in the intake pipe and manifold. An intercooler may be disposed in the intake pipe, between the compressor and the intake manifold, to reduce the temperature of the air. The turbine may be a variable geometry turbine (VGT) with an actuator arranged to move the turbine vanes to alter the flow of the exhaust gasses, thereby regulating the rotational speed of the compressor.
The air charging system may further include an exhaust gas recirculation (EGR) pipe coupled between the exhaust manifold and the intake manifold to recirculate a portion of the exhaust gasses back to the combustion chambers, in order to reduce the nitrogen oxides (NOx) emissions. An EGR valve is generally disposed in the EGR pipe with an actuator arranged to move the valve member to regulate the flow of exhaust gasses towards the intake manifold.
During the operation of the engine, the EGR valve actuator, the VGT actuator and the intake valve actuator are generally used to regulate a number of output parameters of the air charging system, particularly the pressure inside the intake manifold, the oxygen concentration inside the intake manifold and the pressure inside the exhaust manifold, in order to vary the air composition and the boost level according to the performance and emissions requirements.
To perform this function, these actuators are controlled by an electronic control unit (ECU) according to separated and uncoordinated control strategies, which are activated and deactivated depending on the current engine operating point, namely on the current values of the engine speed and of the engine load. By way of example, if the current engine operating point is within a region of engine speed and engine load values that requires low pollutant emissions, then the EGR valve actuator is generally controlled with a dedicated closed loop control strategy whereas the VGT actuator is controlled with a simple open loop control strategy. If conversely the current engine operating point is within a region of engine speed and engine load values that requires maximum engine performances, then the EGR valve actuator is controlled with a simple open loop strategy and the VGT actuator is controlled with a dedicated closed loop strategy.
However, the effects generated on the output parameters of the air charging system by the EGR valve actuator, the VGT actuator and the intake valve actuator are generally strictly interdependent and have mutual interactions. As a consequence, the separated and uncoordinated control approach that is conventionally implemented may sometimes be afflicted with low accuracy, especially during fast transients. Moreover, this control approach needs a vast calibration activity to guarantee an acceptable trade-off between engine performances and pollutant emissions in any operating conditions.